This invention generally relates to cargo containers, and more specifically, to the corner construction of modular, stackable cargo containers.
Cargo is frequently shipped in bulk box-shaped containers to reduce handling and to expedite loading and unloading operations. Such containers are often handled by a spreader bar that, in turn, is carried by a crane and superimposed over the containers to engage complementary holding means on the tops of the containers. More specifically, containers of the above-mentioned general type usually include four top corner members, and a spreader bar typically includes four downwardly extending projections or arms that are spaced so that they can be simultaneously inserted into the top corner members of the container. Once inserted into these corner members, the arms of the spreader bar are usually twisted to lock those arms to the corner members so that the spreader bar may be used to carry or lift the container to another location, such as onto a railroad car or onto a ship.
Movement of the twist arms of the spreader bar into the container corner members is usually controlled by a crane operator who may be quite a distance from the container and the spreader bar themselves. As a result, it is difficult to lower the spreader bar so that the locking arms are directly inserted into the co-operating corner members of the containers, and often those arms strike against the roofs of the containers adjacent the corner members. Over time, repeated impacts against a container roof may cause hairline cracks or other small perforations in that roof, allowing liquids such as water to leak into the container. These hairline cracks and perforations are usually very difficult to detect, and often they are only detected after there has been water damage to the container contents.
Cargo containers of the above-mentioned type also often include four bottom corner members that are used to lock the containers onto a support member, which may be, for example, a truck chassis, a railroad car or another modular container. In a typical operation, this support member, whatever it might be, includes four upwardly extending locking pins, and a container is lowered onto or between these locking pins so that they are, or subsequently are, inserted into the bottom corner members of the container. After this, the locking pins may be twisted or turned to lock the container securely to the supporting device. This operation also is normally controlled by a crane operator who lowers the container onto the support member from a distance.
Under the best of conditions, it is difficult to lower the container so that it does not strike the locking pins, and various factors completely outside the control of the crane operator may make this task even more difficult. For instance, a gusty wind may cause a container to swing unevenly as it is lowered onto a railroad car, making it very difficult to position the container directly between container locking pins on the car. Also, when lowering a container onto a ship, wave action may cause the ship to sway enough so that it becomes extremely difficult to position the container directly on the desired location. Consequently, the locking pins on the supporting device occasionally strike the bottom of the floor of the container, adjacent its corner members, and repeated impacts can cause small cracks or perforations in the container floor. Such defects are difficult to observe; and, as with similar defects in the roof of the container, often damage to the container cargo is the first indication that such a crack or perforation may exist.